JP4293597B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus (for example, a copier, a printer, a facsimile apparatus, and an apparatus that combines these functions) that forms an image by a process that requires thermal fixing such as an electrophotographic process. The present invention relates to the image forming apparatus having a function of controlling power supply (lighting) to the heater so as not to be affected by control system characteristics and power supply fluctuations when controlling the fixing heater to a target temperature.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an apparatus for forming an image by an electrophotographic process, a toner image is fixed on a transfer paper by thermocompression bonding. The fixing unit of the image forming apparatus uses a heater for heating and obtains a necessary heating state by controlling the lighting of the heater. As a general control method, a method of changing a heater lighting time (lighting duty (duty)) within a predetermined control time by a control value set to obtain an appropriate heater output is used. .
For example, when controlling the heater lighting so that the temperature at the position where the temperature sensor in the fixing unit is attached is set to a predetermined (target) temperature, the difference between the set temperature and the current temperature or the gradient of the temperature rise In addition, the lighting duty of the heater is changed and controlled. In the method of feeding back the difference between the set temperature and the current temperature, P (proportional) control that determines the lighting time by an amount obtained by multiplying the difference by a proportional constant (parameter), PI (proportional / integral) control that takes temperature transition into account, time A general automatic control method such as PID (proportional / integral / derivative) control that also considers response is applied. The control of the heater lighting duty makes it possible to reach and maintain the temperature at the set temperature quickly and without causing unnecessary overshoot.
[0003]
By the way, the constant (parameter) for determining the lighting duty is designed so as to have a value that suppresses the influence in consideration of variations of elements constituting the control system.
For example, since variations in temperature detection elements and heaters constituting the control system are managed as part specifications, normally, output design specifications do not deviate from these element variations. However, in reality, the greater the variation, the lower the control accuracy and followability, and the possibility of exceeding the amount of variation considered cannot be denied.
In addition, in the case of power supply conditions that are one of the elements, even if the design is specified with ±% of the rated input (AC100V in Japan), it does not cover all the user's conditions. There is no denying the possibility that this will not happen.
In such a case, there is a problem that a target heater output cannot be obtained.
[0004]
Various methods have been proposed so far in order to eliminate the influence on the output due to the above-described variation factors and obtain a target heater output. Such conventional examples can be shown in the following “Patent Documents 1 to 3”.
In “Patent Document 1”, the rate of temperature increase from the start of energization to the control temperature (target temperature used for fixing) is obtained, and a control pattern prepared in advance is selected based on the obtained result, thereby varying the heater resistance value. An example is shown in which a power supply mode in which the wave number and phase control of the power supply waveform to the heater are changed is prepared as a control pattern, and an appropriate operation is enabled by the selection.
In “Patent Document 2”, the temperature rise gradient is measured as a countermeasure for the time delay of the thermistor output for detecting the temperature of the heater heating section, and the thermistor output is corrected and the rise value obtained as a correction value is assumed. A control method that detects the fluctuation of the input voltage by the temperature gradient and obtains the ON / OFF duty of the heater corresponding to the fluctuation by referring to the difference table prepared in advance by the detected value (temperature increase gradient) and the current temperature. It is shown that this method can suppress the influence of fluctuations in the input voltage.
In “Patent Document 3”, temperature rise data with respect to the heater lighting time within a predetermined time is collected, characteristic curve data indicating the relationship between them is obtained, and the rise temperature necessary up to the current measured temperature and the target temperature is obtained. The characteristic curve shows that the temperature control method of determining the heater lighting time as the control amount is used, and this method makes it possible to control the temperature appropriately for the characteristic variation such as the thermal conductivity of the thermal fixing device, and the thermal fixing. It is said that optimization can always be realized even if the device is replaced.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-100755
[Patent Document 2]
Japanese Patent Laid-Open No. 10-161466
[Patent Document 3]
Japanese Unexamined Patent Publication No. 2000-147942
[0006]
[Problems to be solved by the invention]
However, the above-mentioned “Patent Document 1” employs a method of selecting a power supply mode that requires a complicated operation such as changing the wave number or phase control of the power supply waveform to the heater. In addition, it is specified that data required for selecting the power supply mode (temperature increase rate) is collected at the timing after starting energization to start up the heater to the control temperature (target temperature used for fixing). Therefore, it is always performed at the time of image formation, and at the time of collection, the heater output cannot be controlled to the target temperature.
In the above-mentioned “Patent Document 2”, it is assumed that the heater ON / OFF duty corresponding to the fluctuation of the input voltage is obtained by referring to a difference table prepared in advance based on the detected temperature rising gradient and the current temperature, and the table method. The control method is adopted. In addition, the detection of the temperature rising gradient including fluctuations in the input voltage must be performed as an operation separate from the control of the heater output to the target temperature, which is a limiting condition, and an example of performing it during standby is shown. However, in this case, for example, this control does not work when the power is turned on in the morning.
In the above-mentioned “Patent Document 3”, in order to obtain the characteristic curve data indicating the relationship of the temperature rise data with respect to the heater lighting time within a predetermined time, in addition to data collection, a complicated calculation process such as a least square method is required. The load on the microcomputer for performing the operation becomes very heavy. When the power is turned on as shown in the embodiment, since the initial operation is being performed other than the fixing control, it is preferable to reduce the load on the microcomputer if possible.
[0007]
As described above, the conventional examples shown in the above-mentioned “Patent Documents 1 to 3” each require a complicated configuration and operation as a control means for avoiding the influence of fluctuations in control system characteristics and power supply. Further, the operation timing also has a problem that there is an obstruction factor for performing the operation at an appropriate timing because the constraint condition is attached.
An object of the present invention is to control the temperature of a fixing heater in an apparatus that forms an image by a process that requires thermal fixing (for example, a copying machine using an electrophotographic method, a printer, a facsimile apparatus, and an apparatus that combines these functions). The present invention has been made in view of the above-mentioned problems of the prior art. The configuration of the control means used for realizing the control operation not affected by the characteristics of the control system and the fluctuation of the power source is simplified. Data acquisition necessary for the temperature control operation can be performed at an appropriate timing, and an operation with less burden on processing is enabled.
[0008]
[Means for Solving the Problems]
  According to the first aspect of the present invention, as an element used in an image forming process that requires thermal fixing, a fixing heater, a temperature sensor for detecting a heating state by the heater, and a detection value of the temperature sensor for setting a heating state at a target temperature An image forming apparatus having a heater control unit that controls a lighting duty of the fixing heater according to the temperature, wherein the heater control unit acquires a temperature-time characteristic of the fixing heater when the fixing heater is turned on under a predetermined control condition. Means and the obtained temperature-time characteristics of the fixing heater andWhen the rated power supply voltage is inputMeans for calculating a lighting duty correction value based on the obtained temperature-time characteristics, and means for applying the calculated correction value to the current lighting duty controlThe heater control means can execute a preheating mode that keeps the heating state by the fixing heater to a minimum, and obtains a temperature-time characteristic of the fixing heater and a lighting duty correction value when starting from the preheating mode. Activate the means to calculateAn image forming apparatus characterized by the above.
[0009]
  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the means for calculating the correction value of the lighting duty is, ConstantTemperature-time characteristics of landing heaterofInclinationUseIt is characterized by this.
  The invention of claim 3 is the image forming apparatus according to claim 1 or 2,Heater controlMeansThe means for acquiring the temperature-time characteristic of the fixing heater and the means for calculating the correction value of the lighting duty are activated in response to an input operation instruction performed at an arbitrary timing.It is characterized by doing.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described based on the following embodiments shown with the accompanying drawings.
In the embodiment described below, the embodiment will be described with a focus on the configuration related to the control unit of the fixing heater, which is a component unique to the present invention, and other components necessary for the configuration of the entire image forming apparatus including the fixing device. Since the constituent elements can be implemented by elements constituting an existing apparatus such as a copying machine or a printer that forms an image by an electrophotographic process, description of those elements is omitted.
FIG. 1 shows a circuit related to the control of the fixing heater of this embodiment.
The circuit shown in FIG. 1 includes a fixing unit 1, an AC control plate 6, and a base engine control unit (hereinafter referred to as “BCU”) 4.
The fixing unit 1 includes a heater 3 and a temperature sensor (detection element) 2 to be controlled. The AC control plate 6 is a drive unit for lighting the heater 3, and the BCU 4 is a drive control unit for the heater 3. Function. The BCU 4 having a function as a drive control unit of the heater 3 is configured by, for example, a microcomputer (microcomputer), and executes a control operation as base engine control according to a program written in a storage medium inside the microcomputer. As a matter of fact, the following control operation relating to the lighting control of the fixing heater can also be performed by installing a program necessary for the execution.
[0013]
The heater 3 is connected to a commercial AC power supply 8 via a bidirectional switching element 7 such as a triac provided on the AC control plate 6 and a current detection fuse (not shown) as a safety circuit. An input / output isolated photocoupler 9 or the like is often used to drive the switching element 7. The CPU 5 mounted on the BCU 4 causes the photocoupler 9 to emit light in response to a signal generated by the secondary power supply, thereby driving the switching element 7. Then, ON / OFF control of lighting of the heater 3 is performed.
The CPU 5 uses the temperature detection signal to generate a control signal for controlling the temperature of the fixing unit 1 (drive signal of the switching element 7 for controlling the lighting of the heater 3), and obtains it from the temperature sensor 2. . The temperature sensor 2 is disposed in the vicinity of the roller surface (belt surface) of the fixing device to be controlled, and generally an inexpensive thermistor is used.
When the thermistor is used, the thermistor 2 has a characteristic that the resistance value changes depending on the detected temperature. Therefore, the temperature can be converted into a corresponding analog voltage, and the converted voltage can be converted into an A / A of the CPU 5 mounted on the BCU 4. By taking in the D input, the temperature can be detected as a digital amount, and the CPU 5 performs control amount calculation processing for controlling to the set (target) temperature.
With the circuit configuration related to the control of the fixing heater as described above, the CPU 5 controls the heater ON / OFF so that the roller (belt) surface temperature of the fixing unit 1 can transition to or be maintained at a predetermined set temperature. Can be done.
[0014]
Next, a control operation unique to the present embodiment performed as the operation of the circuit (FIG. 1) configured as described above will be described in detail.
The basic control uses the same control method as in the conventional method (see [Conventional Technology] section) to which the above-described general automatic control technology is applied. For example, taking P control as an example, first the temperature is detected by the thermistor 2, the difference between the detected temperature and the set target temperature is obtained, and the lighting duty (time) of the heater is determined by a value obtained by multiplying the difference by a proportional constant Kp. Will be determined.
FIG. 2 is a diagram for explaining the operation of the heater that is ON / OFF controlled according to the lighting duty. As shown in the figure, a certain control unit time t₀Is the control unit, so the time t₀The temperature is detected by the thermistor every time, and t is detected based on the detected temperature and the set target temperature.₀As a value that determines how much time in the cycle is lit, the lighting duty (t_n/ T₀) And the ON / OFF period is determined in each cycle according to this value (t₁, T₂, T₃, ...) will be controlled.
At this time, the larger the difference from the set target temperature, the longer the lighting time, and the smaller the difference from the set target temperature, the shorter the lighting time. The control unit time is determined from the required setting resolution of the CPU performance and lighting time.
The above is a case where the basic control is the P control. If the lighting duty is determined by the microcomputer (CPU 5) in consideration of the temperature transition and the temperature change rate with the control system as it is, the PI control and the PID control are performed.
[0015]
The above control operation has been established as a conventional method, but the control constants Kp, Ki, and Kd of P control, PI control, and PID control each represent the tolerance (variation) of the elements constituting the control system. It is common to design in consideration. However, the variation caused by such considerations is applied to each device to be controlled, and as a result, in the control system of such a design, the heater output after duty control (the amount of heater heat supplied) ) May vary depending on the device.
In the present invention, one of the problems to be solved is to prevent the variation in the control system elements as described above from affecting the control operation amount. In the present embodiment, optimal control in the usage environment of the heater is performed. In order to realize this, this variation is suppressed by correcting the heater lighting duty.
Further, the data collection necessary for performing this correction, the calculation of correction data (correction coefficient described later), etc. are set in the adjustment mode by the CPU 5, and the correction process for the heater lighting duty is cut off from the correction process before the correction process is actually performed. Prepare as a procedure that can be executed separately. Further, in this adjustment mode, the variation of the power supply voltage, which is another problem for performing appropriate temperature control, is also collected by collecting the data that enables the correction, thereby solving the problem.
The specific example shown below shows an example in which the heater heat quantity is corrected so as not to fluctuate due to the variation (tolerance) of the heater output that is a control system element.
[0016]
Here, the adjustment mode will be described.
In the adjustment mode, the temperature-time characteristic of the heater is acquired as data necessary for correcting the heater lighting duty, and a correction value to be applied to the lighting duty is calculated.
The procedure for acquiring the temperature-time characteristics is to turn on the heater first, count the time until the thermistor detection temperature reaches a certain temperature from a certain temperature, finish collecting the necessary data, and based on the collected data Temperature-time characteristics.
FIG. 3 illustrates the detected temperature-time characteristic obtained by the change in the detected value of the thermistor in the adjustment mode.
In the example shown in FIG. 3, the meaning of the temperature-time characteristic and how to obtain it will be described in detail. In the example shown in the figure, the temperature transition time from 50 ° C. to 100 ° C. is measured, and the measured value is obtained as the characteristic value. obtain. The value obtained in this way can be regarded as “time / temperature” (slope) if the temperature transition time or temperature-time has a linear (primary line) relationship. The larger the inclination is, the lower the heater output is, that is, there are variations in control system elements and power supply variations.
When the temperature-time characteristic is represented by a “time / temperature” slope, the temperature-time characteristic can be measured in an arbitrary temperature range, and is closer to a correct value as the temperature difference is larger. If the temperature range is made constant, such as from 50 ° C. to 100 ° C., the measured time can be handled as a characteristic value as it is.
The specific operation in the example shown in FIG. 3 is that the thermistor detection temperature is monitored by the CPU 5 after the heater is turned on, the timer in the CPU 5 is started at the time Ta when 50 ° C. is detected, and the time Tb when 100 ° C. is detected. The timer is stopped at, and then the heater is turned off. The time τ measured by the timer in this operation is τ = Tb−Ta. In this adjustment mode, the heater output needs to be a fixed lighting duty, and a desirable condition is to select a duty in which the transition of the detected temperature of the thermistor becomes a linear straight line as shown in FIG. In Fig. 3, the time between 50 ° C and 100 ° C is measured. However, the temperature-voltage characteristics of the thermistor may be in a section where the error is linear and there is little error, and it is not necessary to limit to 50 ° C-100 ° C.
[0017]
Temperature transition time τ measured under such conditions, standard characteristics measured in advance, ie, rated power supply voltage V₀(Temperature transition time τ obtained under the same measurement conditions in Japan (100 [V])₀And time τ, τ₀Power supply voltage V and rated power supply voltage V supplied to the heater during each measurement₀The relationship of the following formula (1) is established between Therefore, the power supply voltage V under the current environment can be obtained based on this relational expression.
V = a · (τ₀/ Τ) ・ V₀  ……… Formula (1)
“A” in the above equation (1) can be set as an arbitrary constant, and by measuring the characteristic of the equation (1) due to variations in power supply voltage in advance, it can be set as a value unique to each control system. You can ask for it.
Once the power supply voltage V under the current environment is obtained, the heater output under that environment can be obtained, and the rated input (power supply voltage V₀) Heater output at W₀When the heater output under the current environment is W, the following equation (2) is established.
W = (V / V₀)^b・ W₀  ……… Formula (2)
Here, b is a value unique to the heater product (usually provided as characteristic data attached to the product).
Therefore, the correction coefficient α of the heater lighting duty can be obtained as the following equation (3) from the above equations (1) and (2).
α = W₀/ W
= 1 / (a · (τ₀/ Τ))^b  ……… Formula (3)
In the present embodiment, the normal heater lighting duty is multiplied by the correction coefficient α obtained by the above equation (3) to correct the lighting duty that enables proper lighting control.
In this way, an output equivalent to the heater output at the rated input can be obtained without being affected by the power supply situation (input voltage) etc. at the place where the device is installed, and without causing a quick and unnecessary overshoot. It is possible to reach and maintain the set target temperature.
[0018]
When the adjustment mode performed by the CPU 5 is performed according to the result obtained by performing the adjustment mode as in the present embodiment, when the power supply circumstances (input voltage) at the time of use of the apparatus are included in the target, the factory shipment is performed. Adjustment at the time is not necessary and should be done at the minimum when installing the device. If it is only at the time of factory shipment, the load on the microcomputer is reduced because the lighting duty is simply multiplied by the correction coefficient α obtained according to the above equation (3) during normal control. However, there may be cases where power supply conditions are used under conditions that change every moment of the day. In such cases, data collection for correction, calculation of correction data (correction coefficient α Calculation).
In such a situation, it is appropriate to automatically perform an operation of updating the correction coefficient α every time image formation (printing) starts. If the correction coefficient α is updated in this way, only the present apparatus is operating at a certain time of the day, but the surrounding apparatus is also operating at a certain time. Even in this situation, the optimum heater lighting duty can be achieved, the output equivalent to the heater output at the rated input can be obtained, and the temperature can be quickly reached and maintained at the set temperature without causing unnecessary overshoot. Is possible.
[0019]
By the way, the correction control using the correction coefficient α of the present embodiment depends on how accurately the temperature-time characteristic shown in FIG. 3 can be obtained, and in order to obtain more accurate characteristic data. When Ta and Tb, which are measurement points in the figure, are further away, that is, the larger the temperature difference, the better.
In order to satisfy this condition, in the present embodiment, the adjustment mode is automatically performed by using the preheating mode that is normally prepared in a copying machine, a printer, or the like that forms an image by an electrophotographic process. To do.
In the preheating mode, the heater control temperature is lower than that in the normal standby mode, and is prepared as a mode for suppressing power consumption in a state where printing is not originally performed. Generally, when there is no printing operation for a certain period of time after the printing is completed, the mode is shifted to the preheating mode. The heater temperature in the preheating mode can take a larger value than the temperature difference ((Tb−Ta), see FIG. 3) that can be set between the standby mode and the start of printing. A temperature-time characteristic will be obtained.
In this way, the adjustment mode is performed during the preheating mode, so that even when the power supply situation has changed, a more optimal heater lighting duty is achieved, and an output equivalent to the heater output at the rated input is obtained. Thus, the temperature can be reached and maintained at the set temperature quickly and without causing unnecessary overshoot.
[0020]
As explained above, the adjustment mode is executed, and the correction coefficient α calculated at the time of execution is applied to the heater lighting duty to correct fluctuations due to fluctuations in control system elements and fluctuations in heater control due to power supply fluctuations. However, the control method that makes it possible to ensure an appropriate control operation has been described. However, other variations in the actual control system include heater output variations (tolerances), temperature detection element variations (tolerances). ) And so on. For example, even if the variation is unique to the apparatus, there is often no problem if it is adjusted at the time of factory shipment.
On the other hand, there may be parts replacement on the market, but in that case, adjustment at the time of parts replacement is necessary. There is a possibility that it is necessary to make an accurate correction every time the power is turned on in the day or at the start of printing.
In the above embodiment, an example in which the adjustment mode is automatically executed every time printing is started or in the preheating mode has been described. However, various other adjustments are required as in the above-described parts replacement. Since a case may occur, in order to cope with such a case, in this embodiment, a factory, a service person, a user, and the like can intentionally perform an adjustment mode when necessary. For example, it is implemented by providing means for giving an instruction to execute the adjustment mode at an arbitrary timing by an input operation. In addition, as a condition for executing the adjustment mode according to the instruction by the operation, a method for checking whether the temperature detected by the temperature sensor is lower than a predetermined value or not and enabling the execution when the temperature is lower than the predetermined value You may take. The predetermined temperature to be checked at this time is determined so that the correction data obtained when the adjustment mode is performed is executed at a temperature at which an error is unlikely to occur, and if this condition is cleared, execution is instructed at an arbitrary timing. It is possible to obtain appropriate data.
In this way, an output equivalent to the tolerance ± 0 product heater output under the rated voltage can be obtained without being affected by fluctuations in the input voltage in the operating environment and variations (within the allowable tolerance) of the heater. Therefore, it is not necessary to consider the component variation as a design condition, so that the design of the control system is facilitated. Also, the resulting temperature control becomes more accurate, and the fixing temperature can be reached and maintained at the set temperature quickly and without causing unnecessary overshoot.
[0021]
【The invention's effect】
  (1) Effects corresponding to the inventions of claims 1 to 3
  In the temperature control of the fixing heater, by correcting the variations in the temperature sensors, heaters, and power sources that make up the control system, the design difficulty can be improved because the variations are taken into account. It is possible to prevent problems such as inability to control when the temperature is exceeded, and the resulting temperature control is more accurate, reaching the fixing temperature to the set temperature quickly and without unnecessary overshoot.・ It can be maintained.
  In addition, by obtaining the correction value automatically when starting up from the preheating mode, it is possible to obtain an accurate correction value, and it is more optimal when the power supply situation has changed. The heater can be turned on and an output equivalent to the heater output at the rated input can be obtained, and the temperature can be quickly reached and maintained at the set temperature without causing unnecessary overshoot.
  In addition, a correction value (correction coefficient α) is applied to normal heater lighting duty in order to cancel variations in control system elements and power supply fluctuations, and the correction value is expressed as a temperature-time characteristic of the heater ( Since the means for obtaining the correction value is separated from the printing operation and configured as another means, the influence of variations in control system elements and fluctuations in the power source as shown in the prior art is considered. The heater control to suppress it requires a complicated configuration and operation, and does not cause any hindrance to perform at an appropriate timing, simplifying the configuration of the control means and enabling operation with less processing burden .
  In addition, since the execution instruction of the operation for acquiring the correction value at an arbitrary timing is given by the input operation, it is possible to achieve optimization in response to various cases where adjustment is required.
[Brief description of the drawings]
FIG. 1 shows a circuit related to control of a fixing heater in an embodiment of the present invention.
FIG. 2 is a diagram illustrating an operation of a heater that is ON / OFF controlled according to a lighting duty.
FIG. 3 illustrates a detected temperature-time characteristic obtained by a change in the detected value of the thermistor in the adjustment mode.
[Explanation of symbols]
1 ... fixing unit, 2 ... temperature sensor (thermistor),
3. Fixing heater,
4 ... BCU (base engine control unit),
5 ... CPU, 6 ... AC control board,
7 ... switching element, 8 ... commercial AC power supply,
9: Photocoupler.

Claims (3)

As elements used in an image forming process that requires thermal fixing, a fixing heater, a temperature sensor that detects a heating state by the heater, and a fixing sensor according to a detection value of the temperature sensor to obtain a heating state at a target temperature. An image forming apparatus having a heater control means for controlling a lighting duty,
The heater control means acquires a temperature-time characteristic of the fixing heater when the heater is turned on under a predetermined control condition, a temperature-time characteristic of the acquired fixing heater, and a temperature previously obtained when a rated power supply voltage is input. Means for calculating a correction value of the lighting duty based on the time characteristics, and means for applying the calculated correction value to the current lighting duty control ,
The heater control means can execute a preheating mode in which the heating state by the fixing heater is kept to a minimum, and calculates the correction value of the means and the lighting duty for obtaining the temperature-time characteristic of the fixing heater when starting from the preheating mode. An image forming apparatus that activates the means . The image forming apparatus according to claim 1,
Said means for calculating a correction value of the turn-on duty, the temperature of Fixing heater - image forming apparatus, which comprises using a gradient time characteristics. The image forming apparatus according to claim 1 or 2,
The heater control means activates the means for obtaining a temperature-time characteristic of the fixing heater and the means for calculating a correction value of a lighting duty according to an input operation instruction performed at an arbitrary timing. Forming equipment.

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